The box label says, "New Boomerang Pet Ball. Really Works!". It is a small teal box that just fits the ball.
What it does
As the name suggests, the ball is a boomerang. It can be thrown, and returns to whoever threw it.
When SpongeBob attempted to get Gary to take a bath, he threw the ball at the bathtub. However, the ball bounced back. Later, Gary threw the box at SpongeBob's head when SpongeBob was begining to walking away.